If you communicate in a language that uses accent or diacritic characters (e.g. German umlaut) ) then using these special characters reduces the number of characters in an SMS from 160 to 70. Therefore if you say wrote a 100 character text that would cost you 2 SMS message charges from your mobile carrier. If you compressed that (stripped out the special characters) then that would only cost you 1 SMS. Thus saves you money.
We ONLY strip out the special characters if it would result in sending less SMS messages. So for example with a text containing say 50 characters there is no need.